using System;

import java.util.Scanner;

class ZombieKing
{
    public static void main(String[] args)
    {
        Scanner scanner = new Scanner(System.in);

        int n = scanner.nextInt();
        scanner.close();

        int hits = 0; 
        int consecutiveHits = 0;  

        while (n > 0)
        {
            hits++;
            consecutiveHits++;

            if (consecutiveHits == 3)
            {
                n -= 12;
                consecutiveHits = 0;  
            }
            else
            {
                n -= 2;
            }
        }

        System.out.println(hits);
    }
}